1. Technical Field
The present invention relates to a cylindrical lithium ion secondary battery, and more particularly, to a cylindrical lithium ion secondary battery comprising electrode tabs welded to uncoated regions of electrode plates, wherein among the above-mentioned electrode tabs, the width of an electrode tab which is positioned at the center of a jelly-roll type structure of an electrode assembly is extended so that the electrode tab also serves as a center pin and has a heat release function, whereby the manufacturing steps and costs for the secondary battery can be reduced because it is not necessary to insert a separate center pin.
2. Description of the Prior Art
In general, a cylindrical lithium ion secondary battery comprises a cylindrical electrode assembly to which a center pin is fitted, electrolyte contained in the electrode assembly, a cylindrical case for receiving the electrode assembly and the electrolyte, and a cap assembly assembled to the top opening of the cylindrical case for sealing the cylindrical case.
Since such cylindrical lithium ion secondary batteries have a capacity of about 2,000 to 2,400 mAh, they are usually used in notebook computers, digital cameras, camcorders or the like, which requires a large capacity of power. Those secondary batteries are assembled and used in a desired form of a battery pack, in which the batteries are connected in series and/or in parallel according to the required level of voltage or power, and a safety device is provided in the battery pack.
In a cylindrical lithium ion secondary battery having a cylindrical center pin which is separately inserted, the center pin is inserted through the center of the electrode assembly so as to prevent the deformation of the electrode assembly, and so as to quickly discharge, to the top side of the battery (i.e., toward the cap assembly), the gas which is produced within the battery due to heat or the like. A space is formed in the central area of the electrode assembly received in the case. Such a space is formed as a result of extracting a shaft which is used when winding the positive electrode plate and the negative electrode plate with a separator interposed between the positive electrode plate and the negative electrode plate. The center pin is formed by rolling up a thin metallic sheet in a cylindrical form in consideration of cost and gas discharge efficiency. However, when the center pin is formed in this manner, a slit having a predetermined width is formed along the opposite ends of the rolled sheet. In order to prevent the formation of such a slit, the center pin may be occasionally formed in a cylindrical single-piece unit from the beginning.
When a center pin is separately fabricated and inserted into the electrode assembly, there is a disadvantage in that the fabrication costs are high, and the insertion step should be performed. In addition, if the battery is impacted due to falling or the like, the center pin may come out of the electrode assembly and strike the safety vent, thereby deforming or fracturing the safety vent.